Production of latent periodic memory patterns in frostable films

ABSTRACT

PRESCREENING TECHNIQUES ARE SET FORTH WHICH PRODUCE LATENT PERIODIC MEMORY PATTERNS IN THE DEFORMABLE SURFACE OF A FROSTABLE RECORDING MEMBER. WHEN THE PRETREATED MATERIAL IS LATER USED IN A CONVENTIONAL FROST IMAGING MODE IT IS FOUND THAT THE PRESCREENED LATENT PATTERN DEVELOPS ON THE FROSTABLE SURFACE AND UNDERGOES AMPLIFICATION UNDER THE INFLUENCE OF THE DEVELOPMENT ENVIRONMENT, FINALLY SERVING AS THE MODULATED CARRIER FOR THE FROST IMAGERY IMPRESSED THEREUPON.

A E. JvlRau 3,560,206

PRODUCTION OF LATENT PERIODIC MEMORY PATTERNS IN FROSTABLE FILMS Filed Dec. 21, 1966 Feb. 2, 1971 FIG.

INVENTOR. ALEX E. JVIRBLIS ATTORNEYS United States Patent Oflice 3,560,206 Patented Feb. 2, 1971 3,560,206 PRODUCTION OF LATENT PERIODIC MEMORY PATTERNS IN FROSTABLE FILMS Alex E. .Ivirblis, Webster, N.Y., assignor to Xerox Corporation, Rochester, N.Y., a corporation of New York Filed Dec. 21, 1966, Ser. No. 603,545 Int. Cl. B41m 5/18 U.S. Cl. 961.1 7 Claims ABSTRACT OF THE DISCLOSURE BACKGROUND OF INVENTION This invention relates generally to deformation imaging and more particularly to methodology and products useful in frost imaging.

In U.S. Pat. No. 3,196,011 to R. W. Gundlach and R. W. Gunther, basic techniques are set forth for thermoplastic imaging processes capable of producing in deformable surfaces continuous tone images corresponding to charge patterns established on the materials by optical and/or electrostatic means. The methods therein set forth generally include su'bsteps whereby a charge density pattern is initially established on the deformable film which is to bear the frost image. Thereafter the film is softenedas by heat vapor or the like-as a result of which forces produced by the variable density charge pattern act to break up the deformable film surface into a pattern of minute light scattering irregularities having a scattering density variation in accord with the original charge pattern.

Subsequent to the discoveries forming the subject matter of the alluded-to Gunther and Gundlach patent it was discovered that if an ordinary screened charge image was imposed upon a frostable film and if furthermore the screen pattern were adjusted so that areas of charge deposition could be placed with greater and lesser spatial frequency, that a hydrodynamically preferred wavelength could be found at which the surface could be made to deform with extreme ease. The screened deformation pattern resulting therefrom would in a crosssectional view be more or less sinusoidal in pattern and thus would grossly resemble the so-called relief patterns also familiar to those schooled in the art of thermoplastic and related deformation imagery. John C. Urbach, Whose discoveries are disclosed in a U.S. Pat. application bearing Ser. No. 476,533 filed Aug. 2, 1965, now U.S. Pat. 3,436,216, entitled, Screened Thermoplastic Deformation Imaging, and assigned to the same assignee as the present application, found that the screened pattern producible at the resonant hydrodynamic frequency referred to, was of enormous utility in that it could utilize as a carrier signal for a modulating frost signal superimposed thereupon. When this type of approach was combined with a highly coherent viewing or projecting arrangement, and where the carrier were in fact periodic, spatial filtering could be thereafter utilized to eliminate the carrier. The advantages derived from such a technique of information recording are enormous in that where a random carrier is used-such as the granular pattern of a silver haloid film or the random de formation of frostthe spectrum thereby resulting will be a continuum inseparable from the modulating signal, as a result of which demodulation of the pattern is essentially impossible, the noisy random carrier being present in and degrading the final images in all instances.

While the Urbach disclosure thus presented a teaching which enormously expanded the capabilities of deformation imaging technology the teaching therein has necessitated that means be provided for establishing the screened deformation pattern that one desires to apply a modulating signal to. The Urbach teaching itself contemplated that the screened pattern could be established by either simultaneously projecting upon a photosensitive and charged frostable receptor a screened pattern and an image pattern from the same projector, or alternatively one could pass the sensitized receptor through adjacent stations, projecting first the screen pattern and therafter the image pattern. While either of these approaches is quite acceptable for laboratory purposes in practical systems the limitations thereby imposed become inacceptable.

In a typical instance for example one may desire to utilize a recording method in accordance with the Urbach teaching in ordinary photographic work in an environment where a relatively conventional camera is required to focus a distant object on a frostable photoreceptor. Under such circumstances it is not practical to utilize the same camera to simultaneously focus the object and the screen on the photo-receptor in that the object plane of the screen being recorded is completely different from the plane of the screen itself. Therefore it becomes necessary to either employ a supplementary lens system to image the screen simultaneously with the imaging of the distant scene or alternatively a separate station is necessary for projection of the screened pattern. In either event the complexity of the camera equipment involved is greatly increased. Furthermore it may be noted that the screening technique described in Urbach requires that the screen image be registered upon the photo-receptor with a degree of precision. This in turn requires sophistication in the lens imaging system and so forth, that one would preferably wish to avoid.

Now in accordance with the present invention I have discovered that it is possible to prescreen frostable imaging devices in such a manner that the prescreened product carries only a latent prescreened pattern. According to the present invention the pattern is provided in a virtually imperceptible form, that becomes intelligible only upon development of the product. This latter feature is important in that were any substantial deformations present at the time of recording of the frost image no one plane would exist at which the record image could be brought to a focus. Additionally it may be noted that if deformations of too large an amplitude are present in the photo-receptor prior to its use, the entire pattern will break up into frost upon subsequent use in a frost mode of imaging, thereby effectively destroying the advantage of the periodic carrier.

In accordance with the foregoing it may be regarded as one object of the present invention to provide a method by which prescreening of frostable films can be achieved.

It is another object of the present invention to provide a prescreening method for frostable films that results in a usable product retaining essentially planar characteristics.

It is a further object of the present invention to provide a frostable medium enabling image recordation on a periodic carrier in the deformable surface thereof, without use of supplementary optical systems for production of the carrier.

It is yet a further object of the present invention to provide frostable recording media which simplify image recording upon periodic carriers formed therein by providing for the manufactured presence therein of such periodic carriers, and in such an incipient form that the imaging qualities of the media remain completely intact.

SUMMARY Now in accordance with the present invention these objects and others as will become apparent in the course of the ensuing specification are achieved through use of screening techniques utilized well in advance of employment of the frostable materials for imaging purposes, which screening techniques produce latent periodic memory patterns on the frostable surface of the recording media. In the simplest instance the effect sought after may be brought about by minute mechanical compression applied to the surface of the frostable product, as for example by gentle contact between the latter and a defraction grating or similar periodic structure. Chemical or photographic means can also be utilized. In any of these cases the resulting latent memory pattern is present, in effect, at a manufacturing stage for the image recording material and is undetectable by most conventional observing methods. When the pretreated material is later used in a conventional imaging modewhich is to say by charging, image exposing, recharging, and developing-it is found that the prescreened latent pattern develops upon the frostable surface and undergoes amplification under the influence of the developing environment, finally serving as the modulated vehicular carrier for the frost imagery impressed thereupon.

BRIEF DESCRIPTION OF DRAWINGS A fuller understanding of the present invention and of the manner in which it achieves the objects previously identified may now best be gained by a reading of the following detailed specification and by a simultaneous examination of the drawings appended hereto in which:

FIG. 1 schematically illustrates the manner in which a defraction grating or other periodic structure may be utilized to produce a latent periodic memory pattern in DESCRIPTION OF PREFERRED EMBODIMENTS In FIG. 1 a typical frostable member 3 is shown having appropriate photoreceptor properties enabling its use in deformation imaging processes. The member 3 is essentially similar to those devices described at great length in the Gunther and Gundlach US. Pat. 3,196,011, previously alluded to. In general such members consist of a conductive substrate 6, an intermediate photoconductive layer 4 comprising for example a thin layer of vitreous selenium or the like, and an overcoated deformable layer 2, which is normally solid and electrically insulating but which may be temporarily softened by the application of heat, solvent vapors or the like. Layer 2 may be opaque when viewed by reflection; otherwise it is normally transparent. The deformable layer 2 as well as the entire frostable member 3 does not per se form part of the present invention. Accordingly no great detail will be indicated here regarding the materials etc. suitable for devising frostable members in accord with member 3 as such details are set forth at great length in the Gunther et a1. patent previously mentioned. So for example a large list of suitable materials for the deformable layer 2 are given at Table I of the aforementioned patent, and the present inventive process would be used to modify the deformable layer 2 regardless of which of these materials were utilized. By way of specific example only the deformable layer 2 in FIG. 1 may be considered to comprise Stabelite 5 or Stabelite 10 both products being rosin ester based compositions available from the Hercules Powder Company under the trade names indicated. It may incidentally be noted that the same technique as will be set forth may be utilized where the frostable members treated comprise other than the three layer structures shown in FIG. 1. By this it is meant to emphasize that the invention is equally applicable to, for example, twolayered structures in which the functions of layers 2 and 4 are combined into a single deformable photoconductor.

In FIG. 1 deformable layer 2 is brought into contact with a defraction grating 5. In the practice of the present invention a small amount of pressure yill be applied between the coupled members 3 and 5, although in many instances the weight alone of defraction grating 5 will be sufficient to produce the effect desired. When the grating 5 is thereafter decoupled from frostable member 3 a visual examination of the surface of the deformable layer 2 will typically reveal no disturbance thereof. Ex-

amination of the surface by conventional optical means including even a microscope or the like will furthermore reveal no change thereof, although in some instances examination by a phase microscope may reveal some shifting of the surface in the area in which contact with the where. This is to say that the member 2 may thereafter be uniformly charged, exposed to a continuous tone pattern of light and shadow, thereafter recharged, and then developed by heat or other means (such as vapor) calculated to soften deformable layer 2. The image that develops as a result of this effort will be just that described in the John Urbach patent application 476,533, now US. Pat. 3,436,216, previously alluded to. This is to say that the resulting image will be a frost signal amplitude modulating a periodic carrier deformation in deformable layer 2, which periodic deformation pattern corresponds in frequency and spacing of peaks to the line spacing of the defraction grating 5 utilized in the pretreatment process. While the mechanical treatment depicted in FIG. 1 has been particularly described in connection with the use of a defraction grating 5, the latter is merely an exemplary structure that exhibits the type of periodic surface discontinuities useful for impressing the desired latent pattern upon the deformable layer 2. In accordance with the teaching of the Urbach application 476,533 the spatial frequency present in the defraction grating, or other periodic structure utilized, will be such as to produce a latent periodic carrier wavelength in the surface of deformable layer 2 from about 1.5 to about ten times the thickness of the layer. As is further taught in Urbach the deformable layer 2 from about 1.5 to about ten times the thickness of the layer. As is further taught in Urbach the deformable layer 2 will normally have a thickness of less than about 2 microns. Thus in a typical combination of parameters found to be effective in the present invention the deformable layer 2 constituted a 1.5-micron thick layer of Stabelite 10, and defraction gratings had a line spacing of approximately lines per millimeter.

The precise mechanism by which latent memory patterns are formed in accord with the present invention is not precisely understood. All that can be said with a degree of certainty is that the disturbances introduced into the frostable surface by the techniques are set forth herein, in some manner or other modify that surface so that development of the latent pattern is thereby enabled. This last consideration can be said to serve as an operational definition of the effect introduced in accord with the present invention. More specifically, one may say that a latent memory pattern is present on a frostable surface when uniform charging and softening of the layer bearing the surface resultsin itself-4n development of a visible pattern corresponding to the latent input. The presence or absence of the latent memory pattern is thus an operationally demonstrable fact.

In FIG. 2 a technique is shown closely related to the method described in connection with FIG. 1; however the FIG. 2 depiction is particularly appropriate for employment during manufacture of the frostable member. Here the conventional conductive base 6 and intermediate photoconductive layer 4 are shown, which elements are identical to similarly identified portions of the FIG. 1 drawing. A toothed doctor blade structure 11, however, is now utilized to simultaneously deposit the deformable layer 2, and to impress upon that layer a latent periodic pattern in accord with the present invention. The doctor blade structure 11 is seen to include a reservoir 12 for the plastic material to be coated upon layer 4. In many instances a heating element may be present in this reservoir to maintain a reasonably fluid condition for the coating materialwhich in such instances will be thermoplastic. The material exudes from slits 13 at the sides of the structure so that the material to be coated effectively covers the blade between the slits 13 and the blade edge 15. This edge 15 is provided with a plurality of teeth 16 which (although greatly magnified in the drawing for purposes of illustration are) once again spaced with a frequency appropriate to introduce the periodic carrier pattern desired in the deformable surface 2 being formed. In practice of the present invention the blade structure 12 is moved in the direction of the arrow as a result of which the material to be coated-which is to say the material which will form the deformable layer 2is both coated upon the layer 4 and impressed with a latent periodic memory pattern by the periodic structure at blade 15.

After the blade structure 12 traverses the surface 4 to provide thereby a frostable member essentially identical to member 3 described in connection with FIG. 1, the deformable layer 2 is allowed to set and the manufacturing step is complete. Once again it may be noted that-as has been indicated in connection with FIG. 1-a visually discernible pattern in deformable layer 2 is found to be lacking. Physically what happens is that the layer 2 as it 1s combed by the toothed blade 15 displays transient channels therein much like the wakes produced by a boats motion through a body of water. As the material takes on a set, however, these channels, for all practical observing purposes, disappear, and as previously indicated can be identified-if at all-only with the aid of sensitive phase microscopes.

In FIGS. 3A, 3B and 3C a series of steps is shown according to which the latent periodic memory patterns of the present invention may be applied through conventional photo-exposure means. In FIG. 3A a frostable member 3 generally in accord with the similarly identified device in FIG. 1 is shown positioned under a conventional enlarger 31 or similar light projective mechanism. A light screen 32 is positioned in the tray of the enlarger, the screen being formed of a series of opaque areas 34 and alternating light transparent areas 33, so that the pattern projected upon the member 3 is a series of alternating light and dark areas. The screen actually utilized will be such as to produce a pattern of alternating light and dark areas upon projection such that the periodicity of successive light (or dark) areas is once again the hydrodynamic resonant frequency suitable for imposing an incipient carrier pattern upon the deformable surface 2.

Prior to the light exposure depicted in FIG. 3A frostable member 3 has been exposed to a corona charging source or the like so that a uniform charge pattern 35 is present on the surface thereof. This prior step is com- :pletely conventional in deformation imaging techniques and accordingly is not explicitly depicted herein. The exposure in FIG. 3A is carried out for sufiicient time to largely dissipate the charge pattern 35 in areas struck by light, after which the member 3 is recharged as shown in FIG. 3B to a uniform electrostatic potential by the positive corona source 36.

So far the process described in connection with FIGS. 3A and 3B is relatively conventional in deformation imaging technology; the distinction from the prior art occurs during the step now shown in FIG. 3C. As is therein shown the frostable member 3 is subjected to a heating source 37, which in an actual experiment took the form of a thermostatically controlled hot-plate. Other conductive or radiant heat sources could of course, be used as well. The application of heat in the present instance is for the purpose of rendering the deformable layer 2 compliant-that is to say that in the illustration shown it is assumed that the layer 2 is thermoplastic in nature and is accordingly softened by the presence of heat. Other softening influencesas for example vapor solvents could similarly be used.

Unlike the case in previous thermoplastic deformation teaching the application of heat in FIG. 3C is continued for a period normally considered insutficient to be of any practical use. By way of a specific example a /2 micron layer of the Stabelite l0 composition previously referenced was overcoated on an 8 to 10 micron photoconductive layer 4 consisting principally of the organic compound 2,5-bis(p-aminophenyl) 1,3,4-oxiadiazole. The lat ter compound is commercially available under the designation to 1920 from the Kalle Company. In the specific experiment cited conductive substrate 6 comprised a /3 inch plate of NES glass (a tin-oxide coated glass product available commercially from the Corning Glass Works, Corning, N.Y.). The hot-plate resembling heat source 37 of FIG. 3C was positioned in thermal contact with the conductive substrate, an intervening layer of water actually being used to assure effective heat transfer. Utilizing thermostatic control to maintain a constant 60 C. temperature, heating of the latent charge image-bearing 'frostable member was continued for a mere /2 sec ond. Under circumstances such as this an image discernable by conventional optical techniques is in no way evident. On the contrary where it is desired to develop a normal deformation image according to the conventional development techniques applicable in the prior art at least a ten second development time has been utilized with parameters similar to those specified in the example.

After the heat or similar softening influence is removed from the vicinity of frostable member 3 the deformable layer 2 is allowed to set and, as has been previously suggested, the incipient pattern present therein is virtually undetectable. However the thus treated member 3 may thereafter be utilized according to conventional frost imaging technology, and it will be found upon development of the electrostatic image formed thereon that the latent carrier pattern develops along with the frost image which modulates the former. It is of important to note here that as is the case with any of the prior embodiments of the present invention, no limitations need be placed upon the time duration present between formation of the latent carrier pattern and the subsequent use of the treated member for conventional frost imaging. The prescreening can therefore be impressed during manufacture of frostable members and the product may thus be made available to a user with the carrier signal already built-in.

While the present invention has been particularly set forth in connection with embodiments utilizing frostable photo-receptors it will be understood by those skilled in the art that similar techniques may be utilized to form latent carrier patterns upon deformation imaging devices lacking photo-receptive qualities. For example, thermoplastic recording members of the type discussed in the 7 Glen Pat. 3,113,179 or the related Boldebuck Pat. 3,063,- 872, wherein conductive foils and thermoplastic surfaces alone are present may also be utilized in connection with the present invention, in that the embodiments of FIGS. 1 and 2 are not dependent in any way upon the photoreceptive properties of the member so treated. Although the present invention has been particularly described in terms of specific embodiments thereof it will be understood in view of the present discolsure that numerous modifications of the present invention may now be readily prepared by those skilled in the art without yet departing from the teaching herein. Accordingly, the present invention is to be broadly constructed and limited only by the scope and spirit of the claims now appended hereto.

What is claimed is:

1. A method for rendering frostable members usable in recording of frost modulated deformation carrier patterns comprising: mechanically impressing upon the deformable imaging layer of said member in advance of frost imaging a periodic pattern characterized by the presence of periodically spaced areas capable of being dveloped in the presence of softening and electrostatic charge into periodic undulations in said deformable layer surface, said periodic undulations being spaced at about 1.5 to times the thickness of said deformable layer, said undulating pattern serving as the carrier signal for said frost image when said member is subsequently used for frost imaging.

2. A method according to claim 1 wherein said periodic pattern is impressed upon said frostable member by contacting the deformable surface thereof with a mechanically periodic structure exhibiting discontinuities with a frequency approximately equal to the resonant frequency of said deformable imaging layer.

3. A method in accordance with claim 2 wherein said mechanically periodic structure comprises a defraction grating.

4. A method according to claim 2 wherein said periodic structure is a toothed doctor blade which is made to simultaneously deposit said deformable layer and form therein a periodic pattern.

5. A method of forming a latent carrier pattern in a frostable member including a deformable layer comprising contacting said layer for a limited period with a structure exhibiting mechanical discontinuities spaced from about 1.5 to 10 times the thickness of the deformable layer.

6. A method in accord with claim 5 wherein said layer has a thickness of approximately 2 microns.

7. Method of deformation recording comprising the steps of:

providing a recording structure having a periodic pattern of mechanical deformations in a deformable imaging layer thereof, said deformations being spaced at about 1.5 to 10 times the thickness of said deformable layer,

amplitude modulating said periodic pattern by means of a frost image.

GEORGE F. LESMES, Primary Examiner M. B. WITTENBERG, Assistant Examiner U.S. Cl. X.R. 

